The invention relates generally to the manufacture of thin film transducers and relates more specifically to processes for lapping thin film transducers. More specifically, the invention relates to methods of monitoring the lapping depth in a thin film transducer having a critical dimension defined by an insulating layer, as well as to a composite lapping monitor.
Rotating disc magnetic recording systems typically employ magnetic head transducers which glide over the magnetic disc media on a cushion of air. The mounting or support structure which carries the transducers are termed xe2x80x9csliders.xe2x80x9d Sliders have air-bearing surfaces that are propelled off the surface of moving media by boundary air which moves with the media disc. The air-bearing surface of a slider is aerodynamically designed to glide on the boundary air due to a pattern of raised rails and recesses which establish the xe2x80x9cfly heightxe2x80x9d of the slider. Read/write transducers are mounted on the rear side of the slider, with the reader sensor and writer gap at the air-bearing surface, facing the moving media.
A slider assembly typically includes a ceramic slider and associated read/write heads, a support flexure arm, interconnection wires between the heads and external signaling devices, and any associated mounting hardware. The slider assembly is mounted on an arm which is movable over the surface of a rotating magnetic disc to position the slider adjacent selected tracks on the disc. Disc drives usually employ multiple discs which rotate together, spaced apart from one another on a single spindle. One slider assembly is provided for each magnetic recording surface in a disc drive.
In magnetic disc drive data storage devices, digital data are written to and read from a thin layer of magnetizable material on a surface of one or more rotating discs. Write and read operations are performed through write and read transducers. The slider and transducers are sometimes collectively referred to as a head, and typically a single head is associated with each disc surface. When the read transducer is a magnetoresistive (MR) type sensor, the combination of the slider and the transducer are frequently referred to as a MR head. The head is selectively moved under the control of electronic circuitry to any one of a plurality of circular, concentric data tracks on the disc surface by an actuator device. Each slider body includes an air bearing surface (ABS). As the disc rotates, the disc drags air beneath the ABS, which develops a lifting force that causes the head to lift and fly above the disc surface.
It is desirable for the air-bearing surface of a slider to fly as close to the media as possible, without actually physically touching the media. Read/write signal strength and bit resolution are dependent on the spacing between the thin layer of magnetizable material on the surface of the rotating disc and the read/write head. A close spacing between the thin layer of magnetizable material on the surface of the rotating disc and the read/write head substantially improves the transducer""s performance. It is also important for the spacing between the slider and media disc to be invariant from the innermost to the outermost diameter data tracks.
Because modern sliders have extremely small fly heights, it is very important that they be accurately machined or lapped. Lapping refers to a process in which a portion of the transducer is ground or otherwise removed in order to achieve a desired dimension within the transducer. The prior art describes lapping methods which utilize resistors that are formed within the thin film transducer to be lapped. Generally, the resistor is positioned such that at least a portion of the resistor will be removed during lapping. As lapping proceeds, part of the resistor is removed, which changes the resistance to electrical flow through the resistor. Once the resistance reaches a predetermined value, lapping can stop as the desired dimension will have been reached.
One known method involves the use of three resistors. Two reference resistors are positioned within a thin film transducer such that they are not effected by a subsequent lapping process. One reference resistor provides a small resistance while the other provides a large resistance. These two resistors are used to calculated the sheet resistance of a composite and from that the target resistance of the third resistor is also calculated. As lapping proceeds, the change of resistance of the third resistor at various places of the lapped wafer, containing a number of transducers, allows adjustment of the lapping rate at different points along the lapped wafer so that the target resistance is reached at the same time for all heads, thereby signaling a stop to the lapping process.
The above-described method generally requires accurate patterning of a conductive strip to function as the lapped resistor and therefore is not feasible for use with transducers relying upon an insulating layer for a critical dimension, such as folded vertical GMR heads. These heads consist of two conducting GMR layers that are partially separated by an insulating layer. For this type of head, the critical distance is the distance between the front edge of the insulating layer and the air bearing surface. Because the critical layer is an insulator, any resistive lapping monitor made from a single conducting layer (as commonly done) would not be accurately aligned with the critical front edge of the insulating layer.
Therefore, there is a need for an accurate way to monitor the lapping depth within transducers in which a critical lapping dimension is defined by an insulating layer, i.e. a folded vertical GMR head.
According to a first aspect of the present invention, there is provided a method of controlling a lapping depth when processing a wafer to produce a thin film transducer having a first insulating layer and at least one non-insulating layer in which a critical dimension is determined by an edge of the insulating layer. The method includes depositing a first conductive layer having a plurality of individual blocks on the wafer and depositing a second insulating layer over at least a portion of the first conductive layer. The method further includes the steps of depositing a second conductive layer having a plurality of individual blocks on the wafer so that the individual blocks of the second conducting layer are offset in relation to the individual blocks of the first conductive layer.
The second insulating layer has an insulating layer edge defining a first region in which the first conductive layer is electrically disconnected from the second conductive layer and a second region in which the first conductive layer is electrically connected to the second conductive layer, thereby providing a composite lapping monitor resistor made up of first conductive layer, the insulating layer and the second conductive layer.
The method also includes steps of providing an electrical current that conducts through the blocks of the first and second conductive layers, the first and second conductive layers providing a resistance to said electrical current, lapping the wafer while monitoring said resistance to said electrical current and stopping lapping once said resistance reaches a predetermined value.
According to another aspect of the invention, there is provided a lapping monitor resistor for monitoring lapping depth in thin film transducers having a first insulating layer and at least one non-insulating layer wherein a critical dimension is determined by an edge of the insulating layer. The monitor includes a first conductive layer having a plurality of conductive blocks, a second insulating layer formed over at least a portion of the first conductive layer, and a second conductive layer having a plurality of conductive blocks, where the second conductive layer is electrically connected to the first conductive layer where the second insulating layer is not formed.
According to yet another aspect of the invention, there is provided a monitor resistor for monitoring lapping depth in thin film transducers. The resistor includes a first and second conductive layer wherein the first and second conductive layers are electrically uncoupled by an insulating layer in a first region and the first and second conductive layers are electrically coupled in a second region. The resistor also includes means for measuring resistance in the second region as the first and second conductive layers are lapped.
The above, as well as additional objects, features, and advantages of the present invention will become apparent in the following detailed written description.